At the present stage of technology there exist three-barrel rifles that are heterogeneous in the sense that at least one of the barrels is of the rifled-bore type and thus is suitable for the firing of single-bullet so-called ball ammunition.
From the point of view of their operation, insofar as they permit a number of shots equal to that permitted by multiple barrel rifles, they are equivalent to semiautomatic rifles which enable one to fire as many as five homologous cartridges one after the other (although Italian law has a limit of three). The automatic rifles with only one barrel have the drawback that they provide the hunter with only with homogenous firing, although it would be very much more convenient to be able to have differentiated firing. This can only be obtained by having a variety of barrels, so that an appropriate neck may be used for each type of munition.
Again, from the point of view of the rifle's operation, there exist cartridges which have fundamentally the same structure as traditional pellet cartridges but which instead contain a single ball and which can therefore be fired from smooth-bore barrels. Also, cartridges that can be fired from rifled-bore barrels are of limited use, especially in terms of compliance with the law, and the rifle desired to fire such cartridges is affected by legal limitations which may also make use of the rifle conditional on blocking up the rifled-bore barrel.